This invention relates to conductive and photonic polymer membrane articles, and methods to fabricate such articles.
A number of studies have shown that conducting polymers processed into films and coatings can be used in a wide variety of applications. These applications include corrosion protection, static dissipation from polymer fibers, textile/fiber reinforcement to provide microwave-absorbing materials with stable radioelectric properties, radar absorbing composites and photovoltaic materials. The principal barrier to the commercial use of conductive polymers in these types of applications and others has been the lack of a viable and economically feasible processing technique that can fabricate these polymers into mechanically tough, stable and high surface area architectures.
Conducting polymer films are typically produced by casting or deposition from solution. Films produced in these manners are fragile, have a relatively low surface area, and are not porous.
Conductive polymers are also spin deposited into coagulating solutions to form conductive fibers. This process produces relatively gross fibers having diameters of around 10-100 um. These fibers are also weak, and have relatively low surface area.
It is therefore a primary object of this invention to provide conductive (electrical, ionic, and photoelectric) membrane articles that are lightweight and porous, yet have high surface area and are mechanically tough. Such articles can also be fabricated on flexible substrates, such as textiles.
It is a further object of this invention to provide conductive membrane articles that can be designed to have a wide range of electrical, ionic and photoelectric conducting properties.
This invention results from the realization that thin nanoporous conductive flexible articles having extremely high surface area, porosity and toughness can be fabricated by electrospinning at room temperature or thereabout a solution comprising of a matrix polymer and/or a conductor (such as a conducting polymer or conductive nanoparticles), to create a conductive (electrical, ionic, and photoelectric) membrane composed of a non-woven mat of fibers having diameters of less than one micron, corresponding to surface areas greater than 10 m2/g.
The invention describes new electrospun conducting polymer membranes and composites that have high surface areas and are lightweight, tunable and active (electrically, chemically and optically). A purpose of this invention is to develop a new technique to process conducting polymers into useful and more efficient architectures for applications including but not limited to, ionic and electrical conductivity, photovoltaic devices, electrostatic dissipation, chemical sensing, corrosion protection, electromagnetic interference shielding and radar attenuation. Another purpose of this invention is to improve the electrospinning process in general, as addition of just a small amount of soluble conducting polymer to the polymer solutions used for spinning (known in the art as xe2x80x9cspin dopesxe2x80x9d) improves fiber formation and morphology without imparting undesired effects to the final membrane. In this invention, conducting polymers (from organic or aqueous solution or as solid dispersions) are added directly into a spin dope mixture and applied to various surfaces, including but not limited to metals, semiconductors, glass and textiles, or processed as stand alone membranes, using electro spinning technologies.
The conducting polymer membranes of the invention have high surface areas and are lightweight, porous and permeable to vapor. These features are unique in the design and production of conductive thin films: the high surface area of the electrospun fiber enhances exposure of photo conductive compounds to important electrochemical reactions within the film; porosity enables the film to be infiltrated by getting liquids such as polyelectrolytes to improve performance and conductivity; increased interfaces allow for more efficient energy conversion; and vapor permeation enables the film constituents to be altered chemically by vapor reactions. These membranes have intrinsic electrical conductivities ranging from (but not limited to) 0.15 to 10xe2x88x926 S/cm depending on the level and concentration of the conducting polymer(s) used in the spin dope, other components added to the spin dope and the architecture of the membranes. Many different polymers and materials can be blended to form unique membranes with improved properties for use in an array of applications. For example, improved properties including but not limited to mechanical toughness, adhesion, conductivity (electrical, ionic and photoelectric), recognition for sensing, and electromagnetic shielding may be built into these membranes through judicious choice of components.
Recent test results have led to the development of electrospinning techniques for the processing of soluble conducting polymers (organic solvent and aqueous based and mixtures thereof) and dispersions into new conducting polymer fibrous membranes and composite structures. The membranes and composites formed with this invention are unique and desirable in that they are nanoporous structures that have extremely high surface area, porosity and tunability (i.e. properties that can be varied over a range of values). These enhancements to date have not been available for the processing of conductive polymers and are extremely valuable for each of the above-mentioned applications. In addition, these electro spun conducting polymer membranes are inexpensive as they can be easily prepared and modified to the desired size and substrate.
These fibrous membranes can be processed at ambient conditions adhering to and forming vapor permeable membranes on a variety of substrates such as clothing or other surfaces, as well as forming stand-alone membranes. The conducting materials can be readily incorporated into fibrous networks with high surface areas without problematic techniques involving solubility and polymer casting of traditional membranes using conducting polymers. These membranes are lightweight and can be tailored for specific properties depending on use. Single or combinations of various conducting polymers can be added to the spin dope thereby adding their novel properties to the membrane. The conducting polymers also have an effect on the electrospinning process itself by acting in the spin dope to optimize fiber formation.
There are numerous embodiments of the invention, as the membranes can be formulated with not only conducting polymers but with a wide variety of other interesting electronic materials. When solubility is an issue, insoluble conductive particulate compounds and inorganic semiconductor nanoparticles can also be captured by the electrospinning techniques described to impart the desired properties of the included material and yet maintain the similar properties of the nanofibrous membrane as described in this disclosure.
This invention can be used for the fabrication of novel conducting materials for electrostatic dissipation, corrosion protection, electromagnetic interference shielding, signature reduction, photovoltaic devices, lightweight batteries, conductive fabrics and chemical and biological sensing. Other potential applications of this invention include the use of a small amount of conducting polymer in the spin dope to improve electrospinning and fiber formation of other desirable polymeric materials.